In high volume manufacturing processes including ion implantation for processing semiconductor substrates increasing ion current continues to be a priority. One ongoing challenge for ion sources is the ability to breakup and ionize molecular gases that are commonly used as a source of dopants to be implanted into substrates. A related problem is the efficiency of producing multiply charge ions from a precursor species. As is well known, in ion implantation systems multiply charged ions may be used as a means to increase ion implantation energy without increasing acceleration voltage. One particular challenge facing the industry is the ability to produce multiply charged dopant ions from molecular precursors. Commonly used ion sources, such as indirectly heated cathode sources may yield, for example, a higher fraction of singly charge ions than desirable.
Ionization of species to a multiply charged state generally proceeds through a stepwise process, in which the precursor molecule is first broken up into constituent neutral atoms. A neutral atom subsequently loses initially one electron as a result of collision with an electron, thereby forming a singly charged ion. The singly charged ion then loses a second electron in a collision with another electron, and so on. To increase the output of multiply charged ions it is desirable to increase the production rates of ions and decrease the loss rates for ions in the stepwise production process. In principle, this may be accomplished in various manners. For one, the energy of electrons in a plasma within the ion source may be increased. The degree of ionization may also be increased, meaning that the fraction of charged particles such as charged molecules to neutral molecules is increased. In addition, minimizing the rate of ion losses due to collisions with neutrals or chamber walls increases net ion production rate. However, in present day IHC ions sources for many ion species ion production is less than desired.